1. Field of the Invention
The present invention relates to a radio-communication system, more particularly to a switching system provided in a digital radio-communication system for switching from one of a plurality of main communication systems to one of a plurality of stand-by communication systems, at a high speed.
2. Description of the Related Art
In general, a digital radio-communication system includes a plurality of main communication systems, a stand-by communication system used for backing-up one of the main communication systems when the main communication system fails, and a switching control system for switching from the main communication system to the stand-by communication system.
Recently, there has been strongly required an increase of a transmission capacity, and thus there has been developed and attempted to increase main communication systems. Accordingly, stand-by communication systems may be increased. In a prior art digital radio-communication system, only a switching from one main communication system to a single stand-by communication system is taken into account. If the prior art switching method is applied to a new digital radio-communication system which includes a plurality of main communication systems and a plurality of stand-by communication systems, and when a plurality of the main communication systems are simultaneously failed and simultaneously switched to a plurality of the stand-by communication systems, the switching may be sequentially carried out the plurality of channel. As a result, the total switching time becomes n.times.T.sub.SW, where n indicates the number of the radio-communication channels to be switched from the main communication systems to the stand-by communication systems, and T.sub.SW represents an actual switching time for each channel. The actual switching time is, for example, approximately 9 ms. If two main communication systems are simultaneously switched to two stand-by communication systems, the total switching time becomes approximately 18 ms. However, the total switching time after detecting a failure of the main communication systems must be within 10 ms, under the requirement of a microwave digital radio-communication system. The switching time T.sub.SW, per se, can not be reduced. Therefore, the prior art switching method suffers from a low switching speed when a failure of two or more main communication systems occurs simultaneously.